m-RNA is formed by?

Correct option is B. Transcription. Transcription is the first step of DNA based gene expression, in which a particular segment of DNA is copied into mRNA by the enzyme RNA polymerase. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript or hnRNA. So, the correct answer is 'Transcription'